The advent of start/stop technology for internal combustion engines is straining the lifespan of existing starter solenoids. In a typical combustion engine application, a starter solenoid may undergo approximately 30,000 actuations over a 15-year vehicle lifespan. Start/stop technology can increase this figure by a factor of 10 or more. The drive toward lightweighting results in lower series resistance, which increases inrush currents. Together, these factors push the upper limits of the copper contactors used in existing starter solenoids.
The lower series resistance, resulting from lightweighting, can mean that inrush current is much higher than anticipated given the amount of torque required to turn over an engine. In one example, the inrush current for a 1.3-liter ICE reached 900 A—50% higher than what was expected for the starting system. These high inrush currents, combined with the increase in starter solenoid actuation cycles, due to start/stop technology, cause traditional copper starter solenoid contactors to wear out prematurely. The electrical arcing resulting from high inrush current yields two predominant failure modes: debris (mostly melted copper particles) can mechanically jam the actuator, or the contact wear can become so severe that the contactor can no longer close. During testing, copper contactors weighing between 350 g and 700 g were unable to reach 30,000 cycles at 950 A inrush current.